Analytical calculation of the RMS current stress on the DC link capacitor for a VSI employing reduced common mode voltage PWM

Abstract

This paper derives a simple analytical expression for the RMS current stress on the DC link capacitor of voltage source inverters which employ the reduced common mode voltage pulse width modulation (RCMPWM) technique. The derivation assumes the DC link voltage is constant and that the PWM switching frequency is high enough such that sinusoidal output currents are achieved. The validity of the derivation is confirmed with numerical simulations. The AC RMS current which must be carried by the DC link capacitor is then a function of the modulation depth and is directly proportional to the output RMS current value. This paper shows that dependant upon power factor, the RMS capacitor current is increased approximately 1.3-2.0 times that obtained with traditional space vector PWM or discontinuous PWM methods.